Add beets to same skillet, tossing to coat with any remaining herbs and oil. Cover skillet with foil and transfer to oven. Roast until beets are tender, about 45 minutes. Cool beets. Peel, if desired; cut in half.

Toss arugula with 1/2 cup dressing in large wide bowl. Season to taste with salt and pepper. Top with beets and croutons and serve.

Test-kitchen tip:
After being roasted, baby beets peel easily, but the skins are perfectly edible if you choose to leave them on.